Apple's iPhone 4 release is due out this summer, and it will bring many long-awaited features to the platform.

For the third year in a row, Apple used an early spring event to give developers a preview of the changes coming to the iPhone OS. In case you missed our live coverage of the event, here's a quick summary of what Apple CEO Steve Jobs and other executives unveiled Thursday in Cupertino.

Apple CEO Steve Jobs unveils iPhone OS 4 Thursday.
James Martin/CNET

Multitasking: iPhone developers and users will finally be able to switch back and forth between applications without having to shut down the app entirely to enter the new one. Probably the biggest development unveiled Thursday, it comes with a catch: iPhone 3G users won't be able to multitask due to hardware restraints.

Folders: Apple's App Store has thousands and thousands of applications sorted in lots of categories, but once those applications made it to the iPhone they were laid out side by side in a checkerboard pattern, forcing users to scroll back and forth across multiple screens. No more: iPhone 4 users will be able to create folders like "Games" and drag and drop apps into those folders, simplifying the home screen.

VoIP and location: Voice-over-Internet-Protocol applications like Skype could be found in the App Store already, but the new OS will make it possible for them to run in the background, mimicking the way the iPhone's native dialer allows users to open up another app while remaining on the phone. And like the VoIP apps, navigation apps and others that need your current location will be able to run in the background while doing other things with the iPhone.

In-box improvements: Unified in-boxes and organize-by-thread features are coming to the iPhone, which will give heavy e-mail users some more options for organizing their e-mail.

iAd: This was perhaps the one announcement where Apple is changing the playing field: it's going to give developers and advertising agencies a way to create in-app advertisements with iAd, giving ads OS-level integration that will expand the creative possibilities. It's a clear shot at Google and its plans to transform its desktop Web ad dominance into the mobile Web, if something that regular users aren't likely to be all that excited about.

Stay tuned for much more coverage on the new software and its impact on users, developers, and the mobile industry.

About the author

Tom Krazit writes about the ever-expanding world of Google, as the most prominent company on the Internet defends its search juggernaut while expanding into nearly anything it thinks possible. He has previously written about Apple, the traditional PC industry, and chip companies. E-mail Tom.
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